Final Report Summary - PI3K / SIGNAL-CANCER (Roles of class I PI 3-kinase isoforms in signalling and cancer)
Inhibitors with activity against one or more PI3K isoforms are currently in phase I trials in cancer. It Is thought that therapeutic interference with the PI3K pathway may have to be targeted at individual PI3K isoforms to overcome toxicity of systemically administered broad-spectrum PI3K inhibitors, especially upon chronic administration, such as in inflammation.
This Marie Curie post-doctoral fellowship was focused on the investigation of PI3K signalling in cancer. Initially, we proposed to investigated:
1. role of PI3K isoforms in transformation;
2. identification of isoform-specific protein kinase / phospho-peptide signatures;
3. impact of multiple PI3K isoforms inactivation; resistance to PI3K inhibitors.
As mentioned in the mid-term report, when dissecting the latest, we surprisingly found that the expression of PI3K C2alpha isoform is highly upregulated in cells chronically treated with PI3K inhibitor. This increased protein expression correlates with increased activity. Furthermore, cells expressing only one allele of PI3K C2alpha exhibit reduced proliferation ability.
Those amazing results raised an important question: Could resistance to PI3K inhibition be mediated by PI3K C2alpha? This hypothesis is of particular interest as this isoform is the ONLY isoform resistant to classical PI3K inhibitor (Coincidence or evolutionary adaptation?) and provided us rational to develop specific inhibitors and study PI3K C2alpha physiology in more details.
Luckily, our lab was generating the first mouse model in which the endogenous PI3K C2alpha is converted into a kinase-dead allele. This strategy, which does not remove the target of interest (as opposed to gene KO), allowed us to investigate the organismal impact of full or partial PI3K-C2a inactivation, without facing compensation by other PI3K family members and also mimicking the impact of systemically administered small molecule inhibitors. I used the second part of my grant to characterise this unique and timely mouse model. While homozygosity for this kinase-dead PI3K C2alpha was embryonic lethal, heterozygous PI3K C2alpha KI mice were viable and fertile. The reasons for embryonic lethality are currently under investigation with a dedicated lab in Cambridge.
During the course of heterozygous mice characterisation, we found that those mice showed early onset leptin resistance, with a primary defect in leptin signaling in the hypothalamus. Indeed, despite a normal body weight and fat mass, young heterozygous mice had higher circulating leptin concentrations than wild-type littermates, and showed mild hyperphagia. We were able to link this leptin resistance to defective leptin responsivess at hypothalamic levels. This led to mild, age-dependent obesity and glucose intolerance, due to a highly selective impairment of insulin-induced glucose uptake in the heart of old mice, with unaffected insulin signaling in other tissues.
Taken together, these data show that PI3K-C2a inactivation modulates leptin action and glucose homeostasis in the ageing heart.
This study allowed us to gain insight PI3K C2alpha physiology but we still have to understand the role played by this isoform in global PI3K activity.
Highlights of heterozygous PI3K-C2alpha KI mice characterisation:
- homozygous PI3K-C2alpha kinase-dead knockin mice are early embryonic lethal;
- heterozygous PI3K-C2alpha KI mice are viable and fertile, with unaltered insulin signalling in liver, skeletal muscle and adipose tissue;
- male heterozygous PI3K-C2alpha KI mice display early onset hypothalamic leptin resistance and develop age-dependent obesity and glucose intolerance;
- glucose intolerance in aged male heterozygous PI3K-C2alpha KI mice is due to a heart-specific defect in insulin-induced glucose uptake.
This Marie Curie post-doctoral fellowship was focused on the investigation of PI3K signalling in cancer. Initially, we proposed to investigated:
1. role of PI3K isoforms in transformation;
2. identification of isoform-specific protein kinase / phospho-peptide signatures;
3. impact of multiple PI3K isoforms inactivation; resistance to PI3K inhibitors.
As mentioned in the mid-term report, when dissecting the latest, we surprisingly found that the expression of PI3K C2alpha isoform is highly upregulated in cells chronically treated with PI3K inhibitor. This increased protein expression correlates with increased activity. Furthermore, cells expressing only one allele of PI3K C2alpha exhibit reduced proliferation ability.
Those amazing results raised an important question: Could resistance to PI3K inhibition be mediated by PI3K C2alpha? This hypothesis is of particular interest as this isoform is the ONLY isoform resistant to classical PI3K inhibitor (Coincidence or evolutionary adaptation?) and provided us rational to develop specific inhibitors and study PI3K C2alpha physiology in more details.
Luckily, our lab was generating the first mouse model in which the endogenous PI3K C2alpha is converted into a kinase-dead allele. This strategy, which does not remove the target of interest (as opposed to gene KO), allowed us to investigate the organismal impact of full or partial PI3K-C2a inactivation, without facing compensation by other PI3K family members and also mimicking the impact of systemically administered small molecule inhibitors. I used the second part of my grant to characterise this unique and timely mouse model. While homozygosity for this kinase-dead PI3K C2alpha was embryonic lethal, heterozygous PI3K C2alpha KI mice were viable and fertile. The reasons for embryonic lethality are currently under investigation with a dedicated lab in Cambridge.
During the course of heterozygous mice characterisation, we found that those mice showed early onset leptin resistance, with a primary defect in leptin signaling in the hypothalamus. Indeed, despite a normal body weight and fat mass, young heterozygous mice had higher circulating leptin concentrations than wild-type littermates, and showed mild hyperphagia. We were able to link this leptin resistance to defective leptin responsivess at hypothalamic levels. This led to mild, age-dependent obesity and glucose intolerance, due to a highly selective impairment of insulin-induced glucose uptake in the heart of old mice, with unaffected insulin signaling in other tissues.
Taken together, these data show that PI3K-C2a inactivation modulates leptin action and glucose homeostasis in the ageing heart.
This study allowed us to gain insight PI3K C2alpha physiology but we still have to understand the role played by this isoform in global PI3K activity.
Highlights of heterozygous PI3K-C2alpha KI mice characterisation:
- homozygous PI3K-C2alpha kinase-dead knockin mice are early embryonic lethal;
- heterozygous PI3K-C2alpha KI mice are viable and fertile, with unaltered insulin signalling in liver, skeletal muscle and adipose tissue;
- male heterozygous PI3K-C2alpha KI mice display early onset hypothalamic leptin resistance and develop age-dependent obesity and glucose intolerance;
- glucose intolerance in aged male heterozygous PI3K-C2alpha KI mice is due to a heart-specific defect in insulin-induced glucose uptake.